Chemiluminescent Reactions of 0,F
The Journal of Physical Chemistry, Vol. 83, No. 19, 1979
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Chemiluminescent Reactions of 02F. 2. Reactions Producing Excited BrF and IF R. D. Coombe" and R. K. Horne Rockwell International Science Center, Thousand Oaks, Californla 9 1300 (Received March 19, 1979) Publication costs asslsted by Rockwell International
Chemiluminescence from electronically excited BrF and IF has been observed from reactions of molecular halides (Br2,Iz, ICl, and HI) with OzF. Much more intense emission is produced by reactions of bromine or iodine atoms with OzFin the presence of excited singlet molecular oxygen. The emission spectra and photon yields of these reactions are consistent with a proposed mechanism in which the X + OzFreactions produce vibrationally excited ground state XFt molecules. These may cross to the A W , ) state (if sufficient energy is available) or be pumped to the B(3110+)state by collisions with excited singlet oxygen. In the reactions of molecular halides with OzF, halogen atoms may be produced via formation and decomposition of a triatomic complex.
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Introduction Measurement of the B(31To+) X(lZ+) emission spectrum of electronically excited C1F was reported in a recent issue of this j0urnal.l The excited ClF was produced by the reaction of chlorine atoms with gas phase OzF radicals in the presence of excited singlet molecular oxygen [OZ*(lAg,l2+)I. This first observation of emission from the C1F mofecule suggests that mechanisms involving the OzF radical may also be used to generate the other halogen monofluorides BrF and IF in their excited B(3110+)states. In this report, we present our observations of OzF reactions which produce these excited species. In contrast to the C1F case, a wealth of spectroscopic data exists concerning the B X transitions in BrF and IF. Detailed studies of these transitions involving chemiluminescence,2~3a b ~ o r p t i o n , and ~ , ~ laser-induced f l u o r e ~ c e n c etechniques ~~~ have been published by a number of authors. In addition, observations of the A(3111) X(lZ+)transition have been reported for both BrF5 and IF,8although the BrF measurement has been the subject of some controversygand has not been reproduced. In view of the existence of this large body of spectroscopic information, the primary thrust of the present experiments was directed toward the nature and efficiency of the mechanisms producing the excited species. We have observed the production of electronically excited BrF B(3110+)from the reactions of 02F with both molecular bromine and a mixture of bromine atoms and excited singlet molecular oxygen. Measurements were made of the emission spectrum of the BrF and the photon yield of the latter process. Similar experiments were performed for analogous reactions producing excited IF. Emissions from electronically excited IF were also observed from reactions of OzF with molecular iodides IC1 and HI as well as 12.
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Experimental Section As in previous experiments, gaseous OzF was generated by the thermal decomposition of solid Oz+AsF6-.1J0 A diagram of the cell used is shown in Figure 1. The Oz+AsF~-restedon two coarse fritted disks (1cm diameter) positioned 2.5-cm upstream of the body of the cell. Dry Nz was passed through these frits to carry the thermal decomposition products of the salt into the cell body, which was a rectangular quartz extrusion with internal dimensions 5.1 cm X 1.3 crn. The vacuum system consisted of a liquid NZ cooled trap and a 300 cfm Stokes Microvac pump. The linear velocity of gases flowing through the cell varied with the total pressure; for typical pressures of -300 mtorr the velocity was -600 cm/s. Cell pressures were measured with an MKS Baratron capacitance manometer, and there was no appreciable pressure drop down 0022-3654/79/2083-2435$0 1.OO/O
the 20 cm length of the rectangular section. OzF was generated when the cell was heated to cause decomposition of the salt. Heat was applied to the cell with ordinary heating tapes, producing -30 mtorr of gaseous decomposition products (a maximum of half of which is OzF) in typical experiments. The presence of O$ in the cell was detected by using the strong absorption of the radical near 200 nrn.'J1 Absorption measurements were made across the long (5.1 cm) dimension of the cell. Reagents were added to the cell through a wedge-shaped injector positioned between the two OzF entry ports (see Figure 1). The injector incorporated an array of slots through which reagents passed into the stream. Visual inspection of flames produced in the cell indicated that this arrangement resulted in rapid mixing. Emissions from within the cell were dispersed by a McKee-Pederson 0.5-m monochromator and detected by a photon-counting apparatus consisting of a cooled RCA C31034 photomultiplier tube, a PAR-1120 amplifier-discriminator, and an SSR1110 counting unit. The entrance slit of the monochromator was positioned such that the cone of sight passed through the short (1.3 cm) dimension of the cell directly over the reagent injector. The time duration of flames produced in the cell was monitored by an array of three RCA IP28 photomultiplier tubes positioned along the length of the cell. Liquid Brz was purified by multiple freeze-pump-thaw cycles at 196 K and subsequently mixed with argon (Matheson U.H.P., 99.999%) in a 35-L vessel prior to use in the experiments. The mixture contained 19% Br2. IC1 (PCR) was purified by degassing at 77 K followed by distillation into a trap at 196 K. As with Br,, a mixture was prepared with argon in a 35-L vessel (3% IC1). A stream of gaseous I, was obtained from a saturator in which N2 (Airco, 99.999%) was passed through a bed of solid Iz (Malinckrodt). The pressure in the saturator was held at -92 torr. Hence, at the normal ambient temperature (293 K) the stream contained -0.3% 12. HI (Matheson) was purified by fractional condensation at 273 and 77 K. A mixture in argon (HI = 12%) was prepared in a 3-L vessel. Nz (Airco, 99.999%), O2 (Airco, 99.998%) and NO (Matheson, 99.0 % ) were used without further purification. Samples of O2+AsF6-and an Fz/N2mixture were prepared and purified at the Rocketdyne Division of Rockwell International.
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Results and Discussion Reactions Producing Excited BrF. Experiments were performed by adding the Br2/Ar mixture (- 10 mtorr) to a stream of diluent oxygen (-250 mtorr) just upstream of the cell. Mixture of these gases with OzF generated in 0 1979 American Chemical Society
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The Journal of Physical Chemistty, Vol. 83, No. 19, 1979
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TO TRAP AND PUMP
TABLE I: Observed Isotope Splittings in the BrF B(3n,'-)-+ X(%+)Emission Spectruma b band 79BrF 81BrF Av AvPalcc~
I
I I
v t NZ
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Figure 1. The reaction cell used in the experiments.
the cell ( 165 nm, i.e., the Suprasil cutoff). The reactant gases were analyzed by gas chromatography combined with mass spectrometry. The peaks were separated on a gas chromatographic column and identified by their mass spectra. Quantitative determinations of impurities were made by using a 5-ft column packed with Porapak QS (80/100 mesh) and were based on peak areas. The purity level and the major impurities found were CH,F, >99.6% (C02,0.1%; CHFB, 0.26%);CHZF2, >99.8% (C02,0.05%; CHF,, 0.1%; C2H3F3,0.05%); CHF3, >99.8% (C02,0.06%;H20,0.13%); CH3CH2F,>99.61% (iso-C4HI0, 0.38%); CH3CHF2, >99.55% (CF2C12, 0.40% ; CH3CFZC1, 0.04%; CHF@12,trace); He, >99.99% was used directly from the cylinder.
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Results and Discussion Various aspects of the experimental conditions, procedure, and treatment of the data are given in ref 4 and 0 1979 American
Chemical Society
